Nickel-chromium-iron-aluminum alloy having good processability, creep resistance and corrosion resistance, and use thereof

ABSTRACT

A nickel-chromium-iron-aluminum alloy contains (in wt. %)&gt;17 to 33% chromium, 1.8 to &lt;4.0% aluminum, 0.10 to 15.0% iron, 0.001 to 0.50% silicon, 0.001 to 2.0% manganese, 0.00 to 0.60% titanium, 0.0002 to 0.05% each of magnesium and/or calcium, 0.005 to 0.12% carbon, 0.001 to 0.050% nitrogen, 0.0001 to 0.020% oxygen, 0.001 to 0.030% phosphorus, not more than 0.010% sulfur, not more than 2.0% molybdenum, not more than 2.0% tungsten, the remainder nickel with nickel ≥50% and the usual process-related impurities, for use in solar power tower plants using nitrate salt melts as the heat transfer medium, wherein the following relations must be satisfied: Fp≤39.9 (2a) with Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C (3a), wherein Cr, Fe, Al, Si, Ti, Mo, W and C is the concentration of the respective elements in % by weight.

The invention relates to a nickel-chromium-iron-aluminum wrought alloyhaving excellent high-temperature corrosion resistance, good creepresistance and improved processability.

Austenitic nickel-chromium-iron-aluminum alloys having different nickel,chromium and aluminum contents have long been used in furnaceconstruction and in the chemical and petrochemical industry. For thisservice, a good high-temperature corrosion resistance and a good hotstrength/creep resistance are required.

Due to their properties, nickel alloys having different nickel, chromiumand aluminum contents are also of great interest with respect to the usein solar tower power plants. These plants consist of a field of mirrors(heliostats), which are disposed around a high tower. Due to themirrors, the sunlight is concentrated on the absorber (solar receiver)mounted at the tip. The absorber consists of a tube system, in which aheat-transfer medium is heated. This medium circulates in a loop havingtemporary storage tanks. Due to a heat-exchanger system, the thermalenergy is converted by means of a generator into electricity in asecondary loop. The heat-transfer medium is especially a salt mixture ofsodium and potassium nitrate salt melts, whereby a maximum servicetemperature of the salt of around 700° C. is obtained, depending on thealloy used for the components (Kruizenga et al., Materials Corrosion ofHigh Temperature Alloys Immersed in 600° C. Binary Nitrate Salt, SandiaReport, SAND 2013-2526, 2013).

At temperatures above 700° C., the potassium nitrate salt meltsdecompose markedly, which greatly increases the corrosion of themetallic tubes. Therefore the maximum service temperature lies between600 and 700° C., depending on material. The materials usually used inthe absorber are, among others, Alloy 800H (material number 1.4876, UNSN08810) or Alloy 625 (material number 2.4856, UNS N06625) (see Table 1).

In general, it must be pointed out that the high-temperature corrosionresistance of the alloys listed in Table 1 increases with increasingchromium content. The Al-containing alloys form a chromium oxide layer(Cr₂O₃) with an underlying aluminum oxide layer (Al₂O₃), which is moreor less closed. Small additions of strongly oxygen-affine elements suchas, for example, yttrium or cerium, improve the oxidation resistance. Inthe course of the service in the area of application for establishmentof the protective layer, the chromium content is slowly consumed. Theuseful life of the material is therefore prolonged by a higher chromiumcontent, since a higher content of the element chromium, which forms theprotective layer, delays the time at which the chromium content goesbelow the critical limit and oxides other than Cr₂O₃ are formed thatare, for example, iron-containing and/or nickel-containing oxides. Afurther increase of the high-temperature corrosion resistance can beachieved by additions of aluminum and/or silicon. Starting from acertain minimum content, these elements form a closed layer underneaththe chromium oxide layer and in this way reduce the consumption ofchromium.

The hot strength and creep strength at the indicated temperatures areimproved by a high carbon content among other possibilities. However,even high contents of solid-solution-strengthening elements such aschromium, aluminum, silicon, molybdenum and tungsten improve the hotstrength. In the range of 500° C. to 900° C., additions of aluminum,titanium and/or niobium may improve the strength by precipitation of theγ′ and/or γ″ phase.

Examples of these alloys according to the prior art are listed in Table1.

Alloys such as Alloy 602 CA (N06025), Alloy 693 (N06693), Alloy 603(N06603) or Alloy 214 (N07208) are known for their excellent corrosionresistance in comparison with Alloy 600 (N06600) or Alloy 601 (N06601),on the basis of a high aluminum content of more than 1.8%. On the basisof its high aluminum content, Alloy 214 has an excellent resistance in60% sodium nitrate/40% potassium nitrate salt melts (Kruizenga et al.,Materials Corrosion of High Temperature Alloys Immersed in 600° C.Binary Nitrate Salt, Sandia Report, SAND 2013-2526, 2013). At the sametime, alloys such as Alloy 602 CA (N06025), Alloy 693 (N06693), Alloy603 (N06603) or Alloy 214 (N07208) exhibit, on the basis of the highcarbon content or aluminum content, an excellent hot strength or creepstrength in the temperature range in which nitrate salt melts are used.Alloy 602 CA (N06025) and Alloy 603 (N06603) still have an excellent hotstrength or creep strength even at temperatures above 1000° C. However,due to the high aluminum contents, for example, the processability isimpaired, wherein the impairment becomes greater with increasingaluminum content (for example, in Alloy 693 (N06693) and Alloy 214(N07208)). The same is true to a greater degree for silicon, which formslow-melting intermetallic phases with nickel. In Alloy 602 CA (N06025)or Alloy 603 (N06603), the cold formability in particular is limited bya high proportion of primary carbides.

WO 2019/075177 A1 discloses a solar tower system that includes theabsorber tube, a storage tank and a heat exchanger, all of which containa molten salt at temperatures of >650° C. as heat-transfer medium,wherein the disclosure states that at least one of the components(absorber tube, storage tank and heat exchanger) is made from an alloythat contains (in mass-%) 25-45% Ni, 12-32% Cr, 0.1-2.0% Nb, up to 4%Ta, up to 1% V, up to 2% Mn, up to 1.0% Al, up to 5% Mo, up to 5% W, upto 0.2% Ti, up to 2% Zr, up to 5% Co, up to 0.1% Y, up to 0.1% La, up to0.1% Cs, up to 0.1% other rare earths, up to 0.20% C, up to 3% Si,0.05-0.50% N, up to 0.02% B and the rest Fe and impurities.

EP 0 508 058 A1 discloses an austenitic nickel-chromium-iron alloyconsisting of (in mass-%) 0.12-0.3% C, 23-30% Cr, 8-11% Fe, 1.8-2.4% Al,0.01-0.15% Y, 0.01-1.0% Ti, 0.01-1.0% Nb, 0.01-0.2% Zr, 0.001-0.015% Mg,0.001-0.01% Ca, max. 0.03% N, max. 0.5% Si, max. 0.25% Mn, max. 0.02% P,max. 0.01% S, the rest Ni including unavoidable smelting-relatedimpurities.

U.S. Pat. No. 4,882,125 B1 discloses a high-chromium-containing nickelalloy, which is characterized by an outstanding resistance tosulfidation and oxidation at temperatures above 1093° C., an outstandingcreep resistance of more than 200 hours at temperatures above 983° C.and a stress of 2000 PSI, a good tensile strength and good elongation,both at room temperature and elevated temperatures, consisting of (inweight-%) 27-35% Cr, 2.5-5% Al, 2.5-6% Fe, 0.5-2.5% Nb, up to 0.1 C,respectively up to 1% Ti and Zr, up to 0.05% Ce, up to 0.05% Y, up to 1%Si, up to 1% Mn and Ni the rest.

EP 0 549 286 discloses a high-temperature-resistant Ni—Cr alloy,containing 55-65% Ni, 19-25%, Cr 1-4.5% Al, 0.045-0.3% Y, 0.15-1% Ti,0.005-0.5% C, 0.1-1.5% Si, 0-1% Mn and at least 0.005% in total of atleast one of the elements of the group that includes Mg, Ca, Ce, <0.5%in total of Mg+Ca, <1% Ce, 0.0001-0.1% B, 0-0.5% Zr, 0.0001-0.2% N,0-10% Co, the rest iron and impurities.

From DE 600 04 737 T2, a heat-resisting nickel-base alloy has becomeknown, containing ≤0.1% C, 0.01-2% Si, ≤2% Mn, ≤0.005% S, 10-25% Cr,2.1-<4.5% Al, ≤0.055% N, in total 0.001-1% of at least one of theelements B, Zr, Hf, wherein the said elements may be present in thefollowing contents: B≤0.03%, Zr≤0.2%, Hf<0.8%, Mo 0.01-15%, W 0.01-9%,wherein a total content of Mo+W of 2.5-15% may be present, Ti 0-3%, Mg0-0.01%, Ca 0-0.01%, Fe 0-10%, Nb 0-1%, V 0-1%, Y 0-0.1%, La 0-0.1%, Ce0-0.01%, Nd 0-0.1%, Cu 0-5%, Co 0-5%, the rest nickel. For Mo and W, thefollowing formula must be satisfied:

2.5≤Mo+W≤15  (1)

DE 102015200881A1 describes a tubular body of austenitic steel for asalt melt, especially absorber tube of a solar receiver having a saltmelt as heat carrier or other tubing for conveying a salt melt, whereinthe steel composition comprises, on a weight basis:

0% to 0.025% C, preferably 0.0095% to 0.024% C;

0.05% to 0.16% N; 2.4% to 2.6% Mo; 0.4% to 0.7% Si; 0.5% to 1.63% Mn; 0%to 0.0375% P; 0% to 0.0024% S; 17.15% to 18.0% Cr; 12.0% to 12.74% Ni;0.0025% to 0.0045% B;

wherein the rest is Fe and possibly common impurities.

DE 102012002514 describes a nickel-chromium-aluminum-iron alloycontaining (in mass-%) 12 to 28% chromium, 1.8 to 3.0% aluminum, 1.0 to15% iron, 0.01 to 0.5% silicon, 0.005 to 0.5% manganese, 0.01 to 0.20%yttrium, 0.02 to 0.60% titanium, 0.01 to 0.2% zirconium, 0.0002 to 0.05%magnesium, 0.0001 to 0.05% calcium, 0.03 to 0.11% carbon, 0.003 to 0.05%nitrogen, 0.0005 to 0.008% boron, 0.0001-0.010% oxygen, 0.001 to 0.030%phosphorus, max. 0.010% sulfur, max. 0.5% molybdenum, max. 0.5%tungsten, the rest nickel and the common process-related impurities,wherein the following relationships must be satisfied: 7.7 C−x*a<1.0with a=PN, when PN>0, or a=0, when PN≥0. Therein x=(1.0 Ti+1.06Zr)/(0.251 Ti+0.132 Zr) and PN=0.251 Ti+0.132 Zr−0.857 N and Ti, Zr, N,C are the concentrations of the elements in question in mass-%.

DE 102012013437B3 describes the use of a nickel-chromium-aluminum-ironalloy containing (in mass-%)>25 to 28% chromium, >2 to 3.0% aluminum,1.0 to 11% iron, 0.01 to 0.2% silicon, 0.005 to 0.5% manganese, 0.01 to0.20% yttrium, 0.02 to 0.60% titanium, 0.01 to 0.2% zirconium, 0.0002 to0.05% magnesium, 0.0001 to 0.05% calcium, 0.03 to 0.11% carbon, 0.003 to0.05% nitrogen, 0.0005 to 0.008% boron, 0.0001-0.010% oxygen, 0.001 to0.030% phosphorus, max. 0.010% sulfur, max. 0.5% molybdenum, max. 0.5%tungsten, the rest nickel and the common process-related impurities,wherein the following relationships must be satisfied: 0<7.7 C−x*a<1.0(2) with a=PN, when PN>0 (3a), or a=0, when PN≤0 (3b) and x=(1.0 Ti+1.06Zr)/(0.251 Ti+0.132 Zr) (3c), wherein PN=0.251 Ti+0.132 Zr−0.857 N (4)and Ti, Zr, N, C are the concentrations of the elements in question inmass-%, for the manufacture of seamless tubes.

DE 1020120111161A1 describes a nickel-chromium-aluminum alloy containing(in mass-%) 24 to 33% chromium, 1.8 to 4.0% aluminum, 0.10 to 7.0% iron,0.001 to 0.50% silicon, 0.005 to 2.0% manganese, 0.00 to 0.60% titanium,respectively 0.0002 to 0.05% magnesium and/or calcium, 0.005 to 0.12%carbon, 0.001 to 0.050% nitrogen, 0.0001 to 0.020% oxygen, 0.001 to0.030% phosphorus, max. 0.010% sulfur, max. 2.0% molybdenum, max. 2.0%tungsten, the rest nickel and the common process-related impurities,wherein the following relationships must be satisfied: Cr+Al≥28 (2a) andFp 5; 39.9 with (3a)Fp=Cr+0.272.Fe+2.36.A1+2.22.Si+2.48.Ti+0.374.Mo+0.538.W−11.8.C (4a),wherein Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of theelements in question in mass-%.

U.S. Pat. No. 5,862,800 A discloses a solar tower power plant forintroduction of solar energy into molten salts, wherein tubes of equaldiameter and equal wall thickness are used that consist of Alloy 625.The composition of Alloy 625 is indicated as follows: Cr 20-23%,Al≥0.4%, Fe≥5%, Si≥0.5%, Mn≥0.5%, Ti≥0.4%, C 0.03-0.1%, P≥0.02%,S≥0.015%, Mo 8-10%, Nb 3.15-4.15%, the rest Ni (≥58%).

The task underlying the invention consists in designing a nickel alloythat has sufficiently high chromium and aluminum contents, so that ithas

-   -   a good phase stability,    -   a good processability,    -   a good corrosion resistance in air, similar to that of Alloy 602        CA (N06025)    -   and a good hot strength/creep strength, in order to supply it to        a different kind of application situation.

This task is accomplished by a nickel-chromium-iron-aluminum alloycontaining (in mass-%) >17 to 33% chromium, 1.8 to <4.0% aluminum, 0.10to 15.0% iron, 0.001 to 0.50% silicon, 0.001 to 2.0% manganese, 0.00 to0.60% titanium, respectively 0.0002 to 0.05% magnesium and/or calcium,0.005 to 0.12% carbon, 0.001 to 0.050% nitrogen, 0.0001 to 0.020%oxygen, 0.001 to 0.030% phosphorus, max. 0.010% sulfur, max. 2.0%molybdenum, max. 2.0% tungsten, the rest nickel with nickel ≥50% and thecommon process-related impurities for the use in solar tower powerplants with use of nitrate salt melts as heat-transfer medium, whereinthe following relationships must be satisfied:

Fp≤39.9 with  (2a)

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C  (3a)

wherein Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of theelements in question in mass-%,wherein Cr, Fe, Al, Si, Ti, Nb, Cu, Mo, W and C are the concentrationsof the elements in question in mass-%.

Advantageous further developments of the subject matter of the inventioncan be inferred from the associated dependent claims.

All values of alloy contents are in mass-% unless otherwise indicated.

The range of values for the element chromium lies between >17 and 33%,wherein preferred ranges may be adjusted as follows:

-   -   >18 to 33%    -   20 to 33%    -   22 to 33%    -   24 to 33%    -   25 to 33%    -   26 to 33%    -   27 to 32%    -   28 to 32%    -   >28 to 32%    -   29 to 31%

The aluminum content lies between 1.8 and <4.0%, wherein here also,depending on service area of the alloy, preferred aluminum contents maybe adjusted as follows:

-   -   1.8 to 3.8%    -   1.8 to 3.2%    -   2.0 to 3.2%    -   2.0 to <3.0%    -   2.0 to 2.8%    -   2.2 to 2.8%    -   2.2 to 2.6%    -   2.5 to <4.0%    -   >3.0-<4.0%    -   >3.2-<4.0%    -   >3.2-3.8%    -   >3.0-<3.5%

The iron content lies between 0.1 and 15.0%, wherein, depending on thearea of application, preferred contents may be adjusted within thefollowing ranges of values:

-   -   0.1-12.0%    -   0.1-10.0%    -   0.1-7.5%    -   0.1-4.0%    -   0.1-3.0%    -   0.1-<2.5%    -   0.1-2.0%    -   0.1-<2.0%    -   0.1-1.0%    -   0.1-<1.0%    -   1.0-15.0%    -   1.25-15.0%    -   >2.5-15.0%    -   >4.0-15.0%    -   >4.0-12.0%    -   >7.0-15.0%    -   >7.0-10.5%    -   7.5-10.5%

The silicon content lies between 0.001 and 0.50%. Preferably, Si can beadjusted within the range of values as follows in the alloy:

-   0.001-<0.40%-   0.001-<0.25%-   0.001-0.20%-   0.001-<0.10%-   0.001-<0.05%

The same is true for the element manganese, which may be contained inproportions of 0.001 to 2.0% in the alloy.

Alternatively, the following range of values is also conceivable:

-   -   0.001-0.50%    -   0.001-<0.40%    -   0.001-0.20%    -   0.001-0.10%    -   0.001-<0.05%    -   0.005-<0.05%

The titanium content lies between 0.00 and 0.60%. Preferably, Ti can beadjusted within the range of values as follows in the alloy:

-   -   0.001-0.60%    -   0.001-0.50%    -   0.001-0.30%    -   0.001-0.10%    -   0.01-0.30%    -   0.01-0.25%    -   0.00-<0.02%

Magnesium and/or calcium is also present in contents of 0.0002 to 0.05%.Preferably, the possibility exists of adjusting these elements in thealloy as follows:

-   -   0.0002-0.03%    -   0.0002-0.02%    -   0.0005-0.02%

The alloy contains 0.005 to 0.12% carbon. Preferably this may beadjusted within the range of values as follows in the alloy:

-   -   0.01-<0.12%    -   0.005-0.10%    -   0.005-<0.08%    -   0.005-<0.05%    -   0.01-0.03%    -   0.01-<0.03%    -   0.02-0.10%    -   0.03-0.10%

This is true in the same way for the element nitrogen, which is presentin contents between 0.001 and 0.05%. Preferred contents may be obtainedas follows:

-   -   0.003-0.04%

Furthermore, the alloy contains phosphorus in contents between 0.001 and0.030%. Preferred contents may be obtained as follows:

-   -   0.001-0.020%

Furthermore, the alloy contains oxygen in contents between 0.0001 and0.020%, especially 0.0001 to 0.010%

The element sulfur is present as follows in the alloy:

-   -   Sulfur max. 0.010%

Molybdenum and tungsten are contained individually or in combination inthe alloy with a content of respectively at most 2.0%. Preferredcontents may be obtained as follows:

-   -   Mo max. 1.0%    -   W max. 1.0%    -   Mo max. <0.50%    -   W max. <0.50%    -   Mo max. <0.10%    -   W max. <010%    -   Mo max. <0.05%    -   W max. <0.05%

Beyond this, the following relationship must be satisfied in order thatadequate phase stability is ensured:

Fp≤39.9 with  (2a)

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C  (3a)

wherein Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of theelements in question in mass-%.

Preferred ranges may be adjusted as follows:

Fp≤38.4  (2b)

Fp≤36.6  (2c)

The nickel content is greater than or equal to 50% or greater than 50%.It may be preferably adjusted as follows:

-   -   ≥55% or >55%    -   ≥60% or >60%    -   ≥65% or >65%    -   ≥68% or >68%

Optionally, the element yttrium may be adjusted to contents of 0.001 to0.20% in the alloy. Preferably, Y can be adjusted within the range ofvalues as follows in the alloy:

-   -   0.001-0.15%    -   0.001-0.10%    -   0.001-0.08%    -   0.001-<0.045%    -   0.01-<0.045%

Optionally, the element lanthanum may be adjusted to contents of 0.001to 0.20% in the alloy. Preferably, La may be adjusted within the rangeof values as follows in the alloy:

-   -   0.001-0.15%    -   0.001-0.10%    -   0.001-0.08%    -   0.001-0.04%    -   0.01-0.04%

Optionally, the element cerium may be adjusted to contents of 0.001 to0.20% in the alloy. Preferably, Ce may be adjusted within the range ofvalues as follows in the alloy:

-   -   0.001-0.15%    -   0.001-0.10%    -   0.001-0.08%    -   0.001-0.04%    -   0.01-0.04%

Optionally, in case of simultaneous addition of cerium and lanthanum,cerium mixed metal (a mixture of around 50% Ce, around 25% La, around15% Pr, around 5% Nd, Sm, Tb and Y) may also be used in contents of0.001 to 0.20%. Preferably, cerium mixed metal may be adjusted withinthe range of values as follows in the alloy:

-   -   0.001-0.15%    -   0.001-0.10%    -   0.001-0.08%    -   0.001-0.04%    -   0.01-0.04%

Optionally, the element niobium may be adjusted to contents of 0.00 to1.10% in the alloy. Preferably, niobium may be adjusted within the rangeof values as follows in the alloy:

-   -   0.001-<1.10%    -   0.001-<0.70%    -   0.001-<0.50%    -   0.001-0.30%    -   0.001-<0.30%    -   0.001-<0.20%    -   0.01-0.30%    -   0.10-1.10%    -   0.20-0.70%

If niobium is contained in the alloy, the formula (3a) must besupplemented as follows by a term for niobium:

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+1.26*Nb+0.374*Mo+0.538*W−11.8*C  (3b)

wherein Cr, Fe, Al, Si, Ti, Nb, Mo, W and C are the concentrations ofthe elements in question in mass-%.

Optionally, the zirconium content lies between 0.001 and 0.20%.

Preferably, zirconium may be adjusted within the range of values asfollows in the alloy:

-   -   0.001-0.15%    -   0.001-<0.10%    -   0.001-0.07%    -   0.001-0.04%    -   0.01-0.15%    -   0.01-<0.10%

Optionally, the hafnium content lies between 0.001 and 0.20%.

Preferably, hafnium may be adjusted within the range of values asfollows in the alloy:

-   -   0.001-0.15%    -   0.001-<0.10%    -   0.001-0.07%    -   0.001-0.04%    -   0.01-0.15%    -   0.01-<0.10%

Optionally, 0.001 to 0.60% tantalum may also be contained in the alloy.

Preferably, Ta may be adjusted within the range of values as follows inthe alloy:

-   -   0.001-0.60%    -   0.001-0.50%    -   0.001-0.30%    -   0.001-0.10%    -   0.001-<0.02%    -   0.01-0.30%    -   0.01-0.25%

Optionally, the element boron may be contained as follows in the alloy:

-   -   0.0001-0.008%

Preferably contents may be obtained as follows:

-   -   0.0005-0.008%    -   0.0005-0.004%

Furthermore, the alloy may optionally contain between 0.0 and 5.0%cobalt, which beyond this may still be limited as follows:

-   -   0.001 to 5.0%    -   0.01 to 5.0%    -   0.01 to <5.0%    -   0.01 to 2.0%    -   0.1 to 2.0%    -   0.1 to <2.0%    -   0.001 to 0.5%

Furthermore, at most 0.5% copper may be contained in the alloy.

Beyond this, the content of copper may be limited as follows:

-   -   max. 0.20%    -   max. 0.10%    -   max. 0.05%    -   <0.05%    -   max. 0.015%    -   <0.015%

If copper is contained in the alloy, the formula (3a) must besupplemented as follows by a term for copper:

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.477*Cu+0.374*Mo+0.538*W−11.8*C  (3c)

wherein Cr, Fe, Al, Si, Ti, Cu, Mo, W and C are the concentrations ofthe elements in question in mass-%.

If niobium and copper are contained in the alloy, the formula (3a) mustbe supplemented as follows by a term for niobium and a term for copper:

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+1.26*Nb+0.477*Cu+0.374*Mo+0.538*W−11.8*C  (3d)

wherein Cr, Fe, Al, Si, Ti, Nb, Cu, Mo, W and C are the concentrationsof the elements in question in mass-%.

Furthermore, at most 0.5% vanadium may be contained in the alloy.

Beyond this, the content of vanadium may be limited as follows:

-   -   max. 0.20%    -   max. 0.10%    -   max. 0.05%

Finally, as impurities, the elements lead, zinc and tin may also bepresent in contents as follows:

-   -   Pb max. 0.002%    -   Zn max. 0.002%    -   Sn max. 0.002%.

Furthermore, the following relationship, which describes a particularlygood processability, may optionally be satisfied:

Fa≤60 with  (4a)

Fa=Cr+20.4*Ti+201*C  (5a)

wherein Cr, Ti, and C are the concentrations of the elements in questionin mass-%.

Preferred ranges may be adjusted with:

Fa≤54  (4b)

If niobium is contained in the alloy, the formula (5a) must besupplemented as follows by a term for niobium:

Fa=Cr+6.15*Nb+20.4*Ti+201*C  (5b)

wherein Cr, Nb, Ti and C are the concentrations of the elements inquestion in mass-%.

Furthermore, the following relationship, which describes a particularlygood hot strength or creep strength, may optionally be satisfied

Fk≥47 with  (6a)

Fk=Cr+19*Ti+10.2*Al+12.5*Si+98*C  (7a)

wherein Cr, Ti, Al, Si and C are the concentrations of the elements inquestion in mass-%.

Preferred ranges may be adjusted with:

Fk≤49  (6b)

Fk≤53  (6c)

If niobium and/or boron is contained in the alloy, the formula (7a) mustbe supplemented as follows by a term for niobium and/or boron:

Fk=Cr+19*Ti+34.3*Nb+10.2*Al+12.5*Si+98*C+2245*B  (7b)

wherein Cr, Ti, Nb, Al, Si, C and B are the concentrations of theelements in question in mass-%.

The alloy according to the invention is preferably smelted in anopen-hearth process, followed by a treatment in a VOD (vacuum oxygendecarburization) or VLF (Vacuum Ladle Furnace) system. However, asmelting and casting in vacuum (VIM) is also possible. After casting iningots or as continuous casting, the alloy is annealed in the desiredsemifinished product mold if necessary at temperatures between 900° C.and 1270° C. for 0.1 hours to 100 hours, then hot-formed, if necessarywith intermediate annealings between 900° C. and 1270° C. for 0.05 hoursto 100 hours. The surface of the material may if necessary be chemicallyor mechanically machined for cleaning intermediately (even severaltimes) and/or at the end. After the end of the hot forming, a coldforming to the desired semifinished product shape may be carried out ifnecessary, with reduction ratios up to 98%, if necessary withintermediate annealings between 700° C. and 1250° C. for 0.1 minutes to70 hours, if necessary under shield gas, such as, for example, argon orhydrogen, followed by a cooling in air, in the agitated annealingatmosphere or in the water bath. Thereafter, a solution annealing iscarried out in the temperature range between 700° C. and 1250° C. for0.1 minutes to 70 hours, if necessary under shield gas, such as, forexample, argon or hydrogen, followed by a cooling in air, in theagitated annealing atmosphere or in the water bath. If necessary,chemical and/or mechanical cleanings of the material surface may becarried out intermediately and/or after the last annealing.

The alloy according to the invention may be readily manufactured andused in the product forms of strip, sheet, rod, wire, longitudinallywelded tube and seamless tube.

These product forms are manufactured with a mean grain size of 5 μm to600 μm. The preferred range lies between 20 μm and 200 μm.

The alloy according to the invention is intended preferably to be usedin solar tower power plants with use of nitrate salt melts as theheat-transfer medium.

It may be used for all components that are in contact with the moltensalt.

It may be used in particular for the absorber (solar receiver) in thetower of the solar power plant and/or for the heat exchanger for thecurrent-generating loop (for example via a steam turbine) and/or for thestorage tank and/or the transport tubes.

The nitrate salts may preferably be a mixture of sodium and potassiumnitrate salts.

The mixture may preferably consist of the following compositions:

-   -   50-70% sodium nitrate and 50-30% potassium nitrate    -   55-65% sodium nitrate and 45-35% potassium nitrate    -   58-62% sodium nitrate and 42-38% potassium nitrate

Alternatively, a mixture of sodium nitrate, potassium nitrate and sodiumnitride may be used.

If necessary, the salt mixtures may also be used under a pure CO₂atmosphere.

The maximum service temperature is 800° C. It may be limited as follows:

-   -   max. 750° C.    -   max. 700° C.    -   max. 680° C.    -   max. 650° C.    -   <650° C.    -   max. 620° C.    -   max. 600° C.    -   <600° C.

Tests Performed Phase Stability

The phases occurring in equilibrium were calculated for the variousalloying variants with the JMatPro program of Thermotech. The TTNI7database of Thermotech for nickel-base alloys was used as the databasefor the calculations.

The formability is determined in a tension test according to DIN EN ISO6892-1 at room temperature. In the process, the offset yield strengthR_(p0.2), the tensile strength R_(m) and the elongation to break A aredetermined. The elongation A is determined on the broken specimen fromthe elongation of the original gauge length L₀ and the gauge lengthafter break L_(U):

A=(L_(U)−L₀)/L₀ 100%=ΔL/L₀ 100%

Depending on gauge length, the elongation to break is provided withindices:

For example, for As, the gauge length L₀=5·d₀, where d₀=startingdiameter of a round specimen.

The tests were performed on round specimens having a diameter of 6 mm inthe measurement region and a gauge length L₀ of 30 mm.

The sampling took place transverse relative to the direction of formingof the semifinished product. The forming speed was 10 MPa/s for R_(p0.2)and 6.7 10⁻³ s⁻¹ (40%/min) for R_(m).

The measured value of the elongation A in the tension test at roomtemperature may be taken as a measure of the deformability.

A readily processable material should have an elongation of at least50%.

The hot strength is determined in a hot tension test according to DIN ENISO 6892-2. In the process, the offset yield strength R_(p0.2), thetensile strength R_(m) and the elongation to break A are determined byanalogy with the tension test at room temperature (DIN EN ISO 6892-1).

The tests were performed on round specimens having a diameter of 6 mm inthe measurement region and a starting gauge length L₀ of 30 mm. Thesampling took place transverse relative to the direction of forming ofthe semifinished product. The forming speed was 8.33 10⁻⁵ s⁻¹ (0.5%/min)for R_(p0.2) and 8.33 10⁻³ s⁻¹ (5%/min) for R_(m) (DIN EN ISO 6892-2).

The specimen is mounted at room temperature in a tension-testing machineand heated without loading by a tensile force to the desiredtemperature. After attainment of the test temperature, a temperatureequilibration is carried out for one hour (600° C.) or for two hours(700° C. to 1100° C.). Then the specimen is so loaded with a tensileforce that the desired elongation rates are maintained and the testbegins.

The creep strength of a material is improved with increasinghigh-temperature strength. Therefore the hot strength is also used forassessment of the creep strength of the various materials.

The corrosion resistance at higher temperatures was determined in anoxidation test at 1000° C. in air, wherein the test was interruptedevery 96 hours and the changes in mass of the specimens due to oxidationwere determined. During the test, the specimens were placed in ceramiccrucibles, so that any oxide spalled off was collected and thus it waspossible to determine the mass of the spalled oxide. The sum of thechange in mass of a specimen (net change in mass) and of the mass of thespalled oxide is the gross change in mass of the specimen. The specificchange in mass is the change in mass relative to the surface area of thespecimens. These are denoted in the following as m_(net) for thespecific net change in mass, m_(gross) for the specific gross change inmass, m_(spall) for the specific change in mass of the spalled oxides.The tests were performed on specimens having a thickness ofapproximately 5 mm. For each batch, 3 specimens were aged, wherein theindicated values are the mean values of these 3 specimens.

Description of the Properties

Corrosion Resistance in Salt Melts

In Kruizenga et al. (2013, Materials Corrosion of High TemperatureAlloys Immersed in 600° C. Binary Nitrate Salt) the nickel alloys Alloy625 (N06625), Alloy 120 (N08120), Alloy 230 (N02230), Alloy 242(N10242), Alloy 214 (N07208) among others (Table 1) were investigatedfor their corrosion resistance in a salt melt, through which air wasbeing passed, of 60% sodium nitrate salt and 40% potassium nitrate saltat 600° C. Table 2 shows the analysis of the alloys used. After the endof the test, the weight of the oxide layer was determined by removing itfrom the surface of the metal and weighing the specimen before the test,after the test and after the removal of the oxide layer. From this, theweight loss (descaling loss) relative to the surface area of thespecimen before the test was determined.

Table 3 shows the corrosion rate after 3000 hours: on the one hand asscaling loss in mg/cm² and on the other hand converted to metal loss inμm/year. The smallest corrosion rate was found for the alloy named Alloy214 with 5.7 μm/year at an aluminum content of 4.5%, followed by Alloy224 with a corrosion rate of 8.3 μm/year at an aluminum content of 3.8%.All other nickel alloys investigated (Alloy 625, Alloy 120, Alloy 242and Alloy 230) have a much higher corrosion rate of 16.8 μm/year andgreater at aluminum contents smaller than 0.5%. Alloy 214 and Alloy 224form an aluminum oxide layer, which develops a good protection againstnitrate salt melts. If the content of aluminum is too low, such as inthe alloys named Alloy 625, Alloy 120, Alloy 242 and Alloy 230, noaluminum oxide layer can be formed, which leads to an increasedcorrosion rate.

Accordingly, it is advantageous that an alloy to be used in nitrate saltmelts have an aluminum content that is sufficiently high that a closedaluminum oxide layer is formed.

The alloy according to the invention has not only an excellent corrosionresistance in nitrate salt melts but at the same time also the followingproperties;

-   -   a good phase stability    -   a good processability    -   a good corrosion resistance in air, similar to that of Alloy        602CA (N06025)    -   a good hot strength/creep strength    -   phase stability

In the nickel-chromium-iron-aluminum system having additions of Tiand/or Nb, various embrittling TCP (topologically close packed) phasescan be formed, depending on alloy contents, such as, for example, Lavesphases, sigma phases or μ-phases or even the embrittling η- or ε-phase(see, for example, Ralf Burgel, Handbuch derHochtemperaturwerkstofftechnik [Handbook of High-Temperature MaterialsEngineering], 3rd edition, Vieweg Verlag, Wiesbaden, 2006, pages370-374). The calculation of the equilibrium phase proportions as afunction of temperature for N06690 in batch 111389, for example (seeTable 4 for typical compositions), theoretically shows the formation ofα-chromium (BCC phase in FIG. 1 ) below 720° C. (T_(s BCC)) insignificant quantitative proportions. The formation of this phase ismade greatly difficult, since it is analytically very different from theprimary material. Nevertheless, if the solvus temperature T_(s BCC) ofthis phase is very high, it is definitely able to form, such asdescribed, for example, in “E. Slevolden, J. Z. Albertsen. U. Fink,“Tjeldbergodden Methanol Plant: Metal Dusting Investigations,”Corrosion/2011, paper no. 11144 (Houston, Tex.: NACE 2011), p. 15” for avariant of Alloy 693 (UNS 06693). FIG. 2 and FIG. 3 show the phasediagrams of the Alloy 693 variants (from U.S. Pat. No. 4,88,125 Table 1)for Alloy 3 and Alloy 10 from Table 4. This phase is brittle and therebyleads to an undesired embrittlement of the material. Alloy 3 has aformation temperature T_(s BCC) of 1079° C., Alloy 10 of 939° C. In “E.Slevolden, J. Z. Albertsen. U. Fink, “Tjeldbergodden Methanol Plant:Metal Dusting Investigations,” Corrosion/2011, paper no. 11144 (Houston,Tex.: NACE 2011), p. 15”, the exact analysis of the alloy in whichα-chromium (BCC phase) forms is not described. It is to be assumed,however, that α-chromium can be formed among the examples cited in Table4 for Alloy 693, in the analyses that theoretically have the highestsolvus temperatures T_(s BCC)(such as, for example, Alloy 10). In acorrected analysis (with reduced solvus temperature T_(s BCC)),α-chromium was subsequently still detected only close to the surface in“E. Slevolden, J. Z. Albertsen. U. Fink, “Tjeldbergodden Methanol Plant:Metal Dusting Investigations,” Corrosion/2011, paper no. 11144 (Houston,Tex.: NACE 2011), p. 15”. In order to avoid the occurrence of such anembrittling phase, the solvus temperature T_(s BCC) in the alloyaccording to the invention should be lower than or equal to 939° C.,which corresponds to the lowest solvus temperature T_(s BCC) among theexamples for Alloy 693 in Table 4 (from U.S. Pat. No. 4,88,125 Table 1).

This is the case in particular when the following formula is satisfied:

Fp≤39.9 with  (2a)

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+1.26*Nb+0.477*Cu+0.374*Mo+0.538*W−11.8*C  (3d)

wherein Cr, Al, Fe, Si, Ti, Nb, Cu, Mo, W and C are the concentrationsof the elements in question in mass-%. Table 4 containing the alloysaccording to the prior shows that Fp is greater than 39.9 for Alloy 8,Alloy 3 and Alloy 2 and is exactly 39.9 for Alloy 10. For all otheralloys having T_(s BCC) lower than 939° C., Fp is ≤39.9.

Processability

The formability will be considered here as an example for theprocessability.

An alloy may be hardened by several mechanisms, so that it has a highhot strength or creep resistance. Thus the alloying of a differentelement leads, depending on element, to a more or less large increase ofthe strength (solution hardening). An increase of the strength by fineparticles or precipitates (particle hardening) is much more effective.This may be done, for example, by the γ′ phase, which is formed withadditions of Al and further elements, such as, for example, Ti to anickel alloy or by carbides, which are formed by addition of carbon to achromium-containing nickel alloy (see, for example, Ralf Burgel,Handbuch der Hochtemperaturwerkstofftechnik [Handbook ofHigh-Temperature Materials Engineering, 3rd edition, Vieweg Verlag,Wiesbaden, 2006, pages 358-369).

The increase of the content of elements that form γ′-phase or of the Ccontent indeed increases the hot strength, but increasingly impairs thedeformability, even in the solution-annealed condition.

For a very readily formable material, elongations A₅ of greater than orequal to 50% but at least greater than or equal to 45% in the tensiontest at room temperature are desirable.

This is achieved in particular when the following relationship betweenthe carbide-forming elements Cr, Nb, Ti and C is satisfied:

Fa≤60 with  (4a)

Fa=Cr+6.15*Nb+20.4*Ti+201*C  (5b)

wherein Cr, Nb, Ti and C are the concentrations of the elements inquestion in mass-%.

Hot strength/creep strength

At the same time, the offset yield strength or the tensile strength athigher temperatures should attain at least the values of Alloy 601 (seeTable 6).

600° C.: offset yield strength R_(p0.2)>150 MPa; tensile strengthR_(m)>500 MPa  (8a,8b)

800° C.: offset yield strength R_(p0.2)>130 MPa; tensile strengthR_(m)>135 MPa  (8c, 8d)

It would be desirable for the offset yield strength or the tensilestrength to lie in the range of the tensile strength of Alloy 602 CA(see Table 6). At least 3 of the 4 following relationships should besatisfied:

600° C.: offset yield strength R_(p0.2)>250 MPa; tensile strengthR_(m)>570 MPa  (9a, 9b)

800° C.: offset yield strength R_(p0.2)>180 MPa; tensile strengthR_(m)>190 MPa  (9c, 9d)

The requirements 8a, 8b, 8c and 8d are met in particular when thefollowing relationship between the principally hardening elements issatisfied:

Fk≤47 with  (6a)

Fk=Cr+19*Ti+34.3*Nb+10.2*Al+12.5*Si+98*C+2245*B  (7b)

wherein Cr, Ti, Nb, Al, Si, C and B are the concentrations of theelements in question in mass-%.

Corrosion Resistance in Air:

The alloy according to the invention is intended to have a goodcorrosion resistance in air, similar to that of Alloy 602 CA (N06025).

EXAMPLES

Manufacture:

Tables 5a and 5b show the analyses of the batches smelted on thelaboratory scale together with some batches of Alloy 602CA (N06025),Alloy 690 (N06690), Alloy 601 (N06601) smelted on the industrial scaleaccording to the prior art and used for comparison. The batchesaccording to the prior art are identified with a T and those accordingto the invention with an E. The batches smelted on the laboratory scaleare marked with an L, the batches smelted on the industrial scale with aG.

The ingots of the alloys in Table 5a and b, smelted on the laboratoryscale in vacuum, were annealed between 900° C. and 1270° C. for 8 hoursand hot-rolled to a final thickness of 13 mm and 6 mm by means of hotrolling and further intermediate annealings between 900° C. and 1270° C.for 0.1 to 1 hour. The sheets produced in this way weresolution-annealed between 900° C. and 1270° C. for 1 hour. The specimensneeded for the measurements were manufactured from these sheets.

For the alloys smelted on the industrial scale, a sample was taken fromthe industrial-scale fabrication of a commercially fabricated sheethaving appropriate thickness. The specimens needed for the measurementswere manufactured from these sheets.

All alloy variants typically had a grain size of 70 to 505 m.

For the exemplary batches in Table 5a and b, the following propertieswere compared:

-   -   Corrosion resistance in nitrate salt melts    -   Phase stability    -   The formability on the basis of the tension test at room        temperature    -   The hot strength/creep resistance by means of hot tension tests    -   The corrosion resistance by means of an oxidation test    -   Corrosion resistance in nitrate salt melts:

In the batches 2301 and 250129 to 250138 and 250147 to 250149, smeltedon the laboratory scale, as well as the batches 250164, 250311 and250526, aluminum is greater than or equal to 1.8%.

This aluminum content is sufficiently high, so that a closed aluminumoxide layer is able to form underneath the chromium oxide layer. Thusthey meet the requirement that was imposed on the corrosion resistancein salt melts.

Phase stability:

For the chosen alloys according to the prior art in Table 4 and for alllaboratory batches (Tables 5a and 5b), the phase diagrams were thereforecalculated and the solvus temperature T_(s BCC) was entered in Tables 4and 5a. For the compositions in Tables 4 and 5a and b, the value for Fpwas also calculated according to formula 3d. Fp becomes greater withincreasing solvus temperature T_(s BCC). All examples of N06693 with ahigher solvus temperature T_(s BCC) higher than that of Alloy 10 have anFp >39.9. The requirement Fp≤39.9 (formula 2a) is therefore a goodcriterion for achieving an adequate phase stability for an alloy. Alllaboratory batches in Tables 5a and b meet the criterion Fp≤39.9.

Formability (processability):

Offset yield strength R_(p0.2), the tensile strength R_(m) and theelongation A₅ for room temperature (RT) and for 600° C. are entered inTable 6, as is further the tensile strength R_(m) for 800° C.

Moreover, the values for Fa and Fk are entered.

In Table 6, the exemplary batches 156817 and 160483 of the alloyaccording to the prior art, Alloy 602 CA, have a relatively smallelongation A₅ at room temperature of 36 and 42% respectively, which liebelow the requirements for a good formability. Fa is greater than 60 andthus above the range that characterizes a good formability. All alloysaccording to the invention (E) exhibit an elongation greater than 50%.Thus they meet the requirements. Fa is smaller than 60 for all alloysaccording to the invention. Thus they lie in the range in which a goodformability is ensured. The elongation is particularly high when Fa isrelatively small.

Hot strength/creep strength

The exemplary batch 156656 of the alloy according to the prior art,Alloy 601 in Table 6, is an example of the minimum requirements ofoffset yield strength and tensile strength at 600° C. and 800° C.; incontrast, the exemplary batches 156817 and 160483 of the alloy accordingto the prior art, Alloy 602 CA, are examples of very good values ofoffset yield strength and tensile strength at 600° C. and 800° C. Alloy601 represents a material that exhibits the minimum requirements of hotstrength and creep strength that are described in relationships 8a to8d. Alloy 602 CA represents a material that exhibits an outstanding hotstrength and creep strength that are described in relationships 9a to9d. For both alloys, the value for Fk is much larger than 47 and forAlloy 602 CA it is additionally even much higher than the value of Alloy601, which reflects the elevated strength values of Alloy 602 CA. Thealloys according to the invention (E) all exhibit an offset yieldstrength and tensile strength at 600° C. and 800° C. in the range of orclearly above that of Alloy 601, and therefore satisfy the relationships8a to 8d. They lie in the range of the values of Alloy 602 CA and, withthe exception of batch 250526 and batch 250311, also meet the desirablerequirements, i.e. 3 of the 4 relationships 9a to 9d. Fk also is largerthan 47 for all alloys according to the invention in the examples inTable 6, or larger than 54 and thus in the range that is characterizedby a good hot strength and creep resistance. Among the laboratorybatches that are not according to the invention, batches 2297 and 2300are an example that does not satisfy the relationships 8a to 8d and alsohas an Fk smaller than 47.

Corrosion resistance in air:

Table 7 shows the specific changes in mass after an oxidation test at1100° C. in air after 11 cycles of 96 hours, i.e. in total 1056 hours.In Table 7, the specific gross change in mass, the specific net changein mass and the specific change in mass of the spalled oxides after 1096hours are indicated. The exemplary batches of the alloys according tothe prior art, Alloy 601 and Alloy 690, exhibit a much higher grosschange in mass than Alloy 602 CA, wherein that of Alloy 601 is in turnmuch larger than that of Alloy 690. Both form a chromium oxide layerthat grows more rapidly than an aluminum oxide layer. Alloy 601 stillcontains approximately 1.3% Al. This content is too small in order toform an even only partly closed aluminum oxide layer, for which reasonthe aluminum in the interior of the metallic material is oxidizedunderneath the oxide layer (internal oxidation). This causes a largeincrease in mass in comparison with Alloy 690. Alloy 602CA containsapproximately 2.3% aluminum. For this alloy, therefore, a closedaluminum oxide layer is able to form underneath the chromium oxidelayer. This reduces the growth of the oxide layer markedly and thus alsothe specific increase in mass. All alloys according to the invention (E)contain at least 2% aluminum and therefore have a similarly small orsmaller gross increase in mass than Alloy 602 CA. Also, all alloysaccording to the invention exhibit spalling in the range of themeasurement accuracy, similarly to the exemplary batches of Alloy 602CA, whereas Alloy 601 and Alloy 690 exhibit great spalling.

The claimed limits for the alloy “E” according to the invention cantherefore be justified individually as follows: Too low chromiumcontents mean that the chromium concentration during use of the alloy ina corrosive atmosphere decreases very rapidly below the critical limit,so that a closed chromium oxide layer can no longer be formed. Thereforea content of >17% chromium is the lower limit. Too high chromiumcontents worsen the phase stability of the alloy, especially at the highaluminum contents of ≥1.8%. Therefore 33% chromium is to be regarded asthe upper limit.

The formation of an aluminum oxide layer underneath the chromium oxidelayer reduces the oxidation rate. Below 1.8% aluminum, the aluminumoxide layer is too incomplete to develop its effect fully. Too highaluminum contents impair the processability of the alloy. Therefore analuminum content of <4.0% forms the upper limit.

The costs for the alloy increase with the reduction of the iron content.Below 0.1%, the costs rise disproportionally, since special primarymaterial must be used. For cost reasons, therefore, 0.1% iron is to beregarded as the lower limit. With increase of the iron content, thephase stability is reduced (formation of embrittling phases), especiallyat high chromium and aluminum contents. Therefore 15% Fe is a practicalupper limit in order to ensure the phase stability of the alloyaccording to the invention.

Silicon is needed for the manufacture of the alloy. A minimum content of0.001% is therefore necessary. Too high contents in turn impair theprocessability and the phase stability, especially at high aluminum andchromium contents. The silicon content is therefore restricted to 0.50%.

A minimum content of 0.001% manganese is necessary for improvement ofthe processability. Manganese is limited to 2.0%, since this elementreduces the oxidation resistance.

Titanium increases the high temperature strength. At 0.60% and above,the oxidation behavior may be impaired, which is why 0.60% is themaximum value.

Even very low magnesium contents and/or calcium contents improve theprocessing by the binding of sulfur, whereby the occurrence oflow-melting nickel-sulfur eutectics is avoided. For magnesium and/orcalcium, therefore, a minimum content of 0.0002% is necessary. At toohigh contents, intermetallic nickel-magnesium phases or nickel-calciumphases may occur, which again greatly worsen the processability. Themagnesium content and/or calcium content is therefore limited to at most0.05%.

A minimum content of 0.005% carbon is necessary for a good creepresistance. Carbon is limited to at most 0.12%, since above such acontent this element reduces the processability by the excessiveformation of primary carbides.

A minimum content of 0.001% nitrogen is necessary, whereby theprocessability of the material is improved. Nitrogen is limited to atmost 0.05%, since the processability is reduced due to the formation ofcoarse carbonitrides.

The oxygen content must be smaller than or equal to 0.020%, in order toensure the manufacturability of the alloy. A too low oxygen contentincreases the costs. The oxygen content is therefore ≥0.0001%.

The content of phosphorus should be smaller than or equal to 0.030%,since this surface-active element impairs the oxidation resistance. Atoo low phosphorus content increases the costs.

The phosphorus content is therefore ≥0.001%.

The content of sulfur should be adjusted as low as possible, since thissurface-active element impairs the oxidation resistance. Therefore atmost 0.010% sulfur is specified.

Molybdenum is limited to at most 2.0%, since this element reduces theoxidation resistance.

Tungsten is limited to at most 2.0%, since this element likewise reducesthe oxidation resistance.

Nickel is the residual element. A too low nickel content reduces thephase stability, especially at high chromium contents.

Nickel must therefore be larger than or equal to 50%.

Beyond this, the following relationship must be satisfied in order thatadequate phase stability is ensured:

Fp≤39.9 with  (2a)

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C  (3a)

wherein Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of theelements in question in mass-%. The limits for Fp and the possibleincorporation of further elements have been justified in detail in theforegoing text.

If necessary, the oxidation resistance may be further improved withadditions of oxygen-affine elements, such as, for example, yttrium,lanthanum, cerium, cerium mixed metal. These elements are incorporatedin the oxide layer, where they block the paths of diffusion of theoxygen at the grain boundaries.

A minimum content of 0.001% yttrium is necessary to obtain the effect ofthe yttrium that increases the oxidation resistance.

For cost reasons, the upper limit is set to 0.20%.

A minimum content of 0.001% lanthanum is necessary to obtain the effectof the lanthanum that increases the oxidation resistance. For costreasons, the upper limit is set to 0.20%.

A minimum content of 0.001% cerium is necessary to obtain the effect ofthe cerium that increases the oxidation resistance. For cost reasons,the upper limit is set to 0.20%.

A minimum content of 0.001% cerium mixed metal is necessary to obtainthe effect of the cerium mixed metal that increases the oxidationresistance. For cost reasons, the upper limit is set to 0.20%.

If necessary, niobium may be added, since niobium also increases thehigh-temperature strength. Higher contents very greatly increase thecosts. The upper limit is therefore set at 1.10%.

If necessary, the alloy may also contain tantalum, since tantalum alsoincreases the high-temperature strength and the oxidation resistance.Higher contents very greatly increase the costs. The upper limit istherefore set at 0.60%. A minimum content of 0.001% is necessary inorder to achieve an effect.

If necessary, the alloy may also contain zirconium. A minimum content of0.001% zirconium is necessary to obtain the effect of the zirconium thatincreases the high-temperature strength and the oxidation resistance.For cost reasons, the upper limit is set to 0.20% zirconium.

If necessary, the alloy may also contain hafnium. A minimum content of0.001% hafnium is necessary to obtain the effect of the hafnium thatincreases the high-temperature strength and the oxidation resistance.For cost reasons, the upper limit is set to 0.20% hafnium.

If necessary, boron may be added to the alloy, since boron improves thecreep resistance. Therefore a content of at least 0.0001% should bepresent. At the same time, this surface-active element worsens theoxidation resistance. Therefore at most 0.008% boron is specified.

Cobalt up to 5.0% may be contained in this alloy. Higher contentsmarkedly reduce the oxidation resistance.

Copper is limited to at most 0.5%, since this element reduces theoxidation resistance.

Vanadium is limited to at most 0.5%, since this element reduces theoxidation resistance.

Lead is limited to at most 0.002%, since this element reduces theoxidation resistance. The same is true for zinc and tin.

Furthermore, optionally the following relationship, which describes aparticularly good processability, may be satisfied for thecarbide-forming elements chromium, titanium and carbon:

Fa≤60 with  (4a)

Fa=Cr+20.4*Ti+201*C  (5a)

wherein Cr, Ti, and C are the concentrations of the elements in questionin mass-%, The limits for Fa and the possible incorporation of furtherelements have been justified in detail in the foregoing text.

Furthermore, optionally the following relationship, which describes aparticularly good hot strength and creep strength, may be satisfiedbetween the elements that increase the strength:

Fk≤47 with  (6a)

Fk=Cr+19*Ti+10.2*Al+12.5*Si+98*C  (7a)

wherein Cr, Ti, Al, Si and C are the concentrations of the elements inquestion in mass. The limits for Fa and the possible incorporation offurther elements have been justified in detail in the foregoing text.

TABLE 1 Alloys according to ASTM B 168-191), ASTM B167-182), ASTMB443-183), ASTM B 163-184), ASTM B622-155), ASTM B409-066). All valuesin mass-%, ⁷⁾ in no ASTM standard, from the UNS list. Legierung Ni Cr CoMo W Nb Nb + Ta Fe Mn Al C Alloy 800H- 30.0- 19.0- 39.5 1.5 0.15- 0.05N08810⁶⁾ ⁴⁾ 35.0 23.0 min max 0.60 0.10 Alloy 600- 72.0 14.0- 6.0- 1.00.15 N06600¹⁾²⁾⁴⁾ min 17.0 10.0 max max Alloy 601- 58.0- 21.0- Rest 1.01.0- 0.10 N06601¹⁾²⁾⁴⁾ 63.0 25.0 max 1.7 max Alloy 617- 44.5 20.0- 10.0-8.0- 3.0 1.0 0.8- 0.05- N06617¹⁾²⁾ min 24.0 15.0 10.0 max max 1.5 0.15Alloy 690- 58.0 27.0- 7.0- 0.5 0.05 N06690¹⁾²⁾⁴⁾ min 31.0 11.0 max maxAlloy 693- Rest 27.0- 0.5- 2.5- 1.0 2.5- 0.15 N06693¹⁾²⁾ 31.0 2.5 6.0max 4.0 max Alloy 602CA- Rest 24.0- 8.0- 0.15 1.8- 0.15- N06025¹⁾²⁾⁴⁾26.0 11.0 max 2.4 0.25 Alloy 603- Rest 24.0- 8.0- 0.15 2.4- 0.20-N06603¹⁾²⁾ 26.0 11.0 max 3.0 0.40 Alloy 699XA- Rest 26.0- 0.50 2.5 0.501.9- 0.005- N06699¹⁾²⁾⁴⁾ 30.0 max max max 3.0 0.10 Alloy 214 Rest 15.0-2.0 0.50 0.50 2.0- 0.50 4.0- 0.05 N07214 ⁷⁾ 17.0 max max max 4.0 max 5.0max Alloy 625- 58.0 20.0- 1.0 8.0- 3.15- 5.0 0.50 0.40 0.10 N06625 ³⁾min 23.0 max 10.0 4.15 max max max max Alloy 120 35.0- 23.0- 3.0 2.502.50 0.4- Rest 1.50 0.04 0.20- N08120⁶⁾⁴⁾ 39.0 27.0 max max max 0.9 maxmax 0.1 Alloy 242 Rest 7.0- 1.0 24.0- 2.5 0.80 0.05 0.03 N10242⁵⁾ 9.0max 26.0 max max max max Alloy 230 Rest 20.0- 4.0 0.30- 13.0- 3.0 0.80-0.20- 0.05- N06230⁵⁾ 24.0 max 3.0 15.0 max 1.0 0.50 0.15 Legierung Cu SiS Ti P Zr Y B N La Alloy 800H-N08810⁶⁾ ⁴⁾ 0.75 1.0 0.015 0.15- max maxmax 0.60 Alloy 600-N06600¹⁾²⁾⁴⁾ 0.5 0.5 0.015 max max max Alloy601-N06601¹⁾²⁾⁴⁾ 0.5 0.5 0.015 max max max Alloy 617-N06617¹⁾²⁾ 1.0 0.50.015 0.6 0.006 max max max max max Alloy 690-N06690¹⁾²⁾⁴⁾ 0.5 1.0 0.015max max max Alloy 693-N06693¹⁾²⁾ 0.5 0.5 0.01 1.0 max max max max Alloy602CA- 0.1 0.5 0.010 0.1- 0.020 0.01- 0.05- N06025¹⁾²⁾⁴⁾ max max max 0.2max 0.10 0.12 Alloy 603-N06603¹⁾²⁾ 0.50 0.5 0.010 0.01- 0.020 0.01-0.01- max max max 0.25 max 0.10 0.15 Alloy 699XA- 0.50 0.50 0.01 0.600.02 0.10 0.008 0.05 N06699¹⁾²⁾⁴⁾ max max max max max max max max Alloy214 N07214 ⁷⁾ max 0.015 0.50 0.015 max 0.002- 0.006 0.2 max max max 0.050.040 max Alloy 625-N06625 ³⁾ 0.50 0.015 0.40 0.015 max max max maxAlloy 120 N08120⁶⁾⁴⁾ 0.50 1.0 0.03 0.20 0.040 0.010 0.15- max max maxmax max max 0.30 Alloy 242 N10242⁵⁾ 0.50 0.80 0.015 0.030 0.006 max maxmax max max Alloy 230 N06230⁵⁾ 0.10 0.25- 0.015 0.030 0.015 0.005- max0.75 max max max 0.05 Legierung = Alloy

TABLE 2 Composition in mass-% of the alloys investigated in (Kruizengaet al., Materials Corrosion of High Temperature Alloys Immersed in 600C. Binary Nitrate Salt, Sandia Report, SAND 2013-2526, 2013). LegierungUNS Cr Mo Ni Mn Si Fe Co W Al Other Alloy214¹⁾ N07214 16 — 75 0.5 0.2 3— — 4.5 Zr(0.1 max) Alloy224²⁾ — 20.50 0.21 46.44 0.33 0.31 27.62 0.38 —3.86 Ti(0.35) Alloy 625²⁾ N06625 21.76 8.28 61.0 0.21 0.25 4.46 0.08 —0.20 Nb(3.38), Ti (0.24) Alloy 120²⁾ N08120 24.91 0.27 37 0.68 0.5036.41 0.15 — 0.08 Alloy242²⁾ N10242 8.05 24.79 65.44 0.29 — 1.24 — —0.13 Cu(0.06) Alloy230²⁾ N02230 22.37 1.27 59.41 0.49 0.42 1.32 0.1914.16 0.32 Cu(0.05) Legierung = Alloy ¹⁾nominal compositions of alloys,²⁾actual composition tested from heat

TABLE 3 Corrosion after 3000 hours in 60% sodium nitrate/40% potassiumnitrate salt melt of the alloys investigated in [Kruizenga et al., 2013,Materials Corrosion of High Temperature Alloys Immersed in 600° C.Binary Nitrate Salt]. Metal loss Density Descaling loss μm/year DichteEntzunderungsverlust¹⁾ Metallverlust¹⁾ Alloy Cr Al Si [g/cm³] [mg/cm²][μm/Jahr] Alloy 214 N07208 16 4.5 0.2 8.05 1.56 5.7 Alloy 224 — 20.53.86 0.31 8^(a)) 2.27 8.3 Alloy 625 N06625 21.76 0.20 0.25 8.44 4.8616.8 Alloy 120 N08120 24.91 0.08 0.50 8.07 4.97 18 Alloy 242 N10242 8.050.13 — 9.05 5.88 18.98 Alloy 230 N02230 22.37 0.31 0.42 8.97 7.25 23.6¹⁾nach 3000 Stunden; ^(a))Dichte angenommen. ¹⁾After 3000 hours;^(a))Density assumed.

TABLE 4 Typical compositions of some alloys according to ASTM B 168-11.and Table 2 (prior art). Legierung Charge C S Cr Ni Mn Si Mo Ti Nb Alloy600 164310 0.07 0.002 15.8 73.8 0.28 0.32 — 0.2 — N06600 Alloy 601156656 0.053 0.0016 22.95 59.58 0.72 0.24 — 0.47 — N06601 Alloy 690111389 0.022 0.002 28.45 61.95 0.12 0.32 — 0.29 — N06690 Alloy 693 Alloy 10 *) 0.015 ≤0.01 29.42 60.55 0.014 0.075 — 0.02 1.04 N06693Alloy 693 Alloy 8 *) 0.007 ≤0.01 30.00 60.34 0.11 0.38 — 0.23 1.13N06693 Alloy 693 Alloy 3 *) 0.009 ≤0.01 30.02 57.79 0.01 0.14 — 0.022.04 N06693 Alloy 693 Alloy 2 *) 0.006 ≤0.01 30.01 60.01 0.12 0.14 —0.01 0.54 N06693 Alloy 602 163968 0.170 ≤0.01 25.39 62.12 0.07 0.07 —0.13 N06025 Alloy 603 52475 0.225 0.002 25.20 61.6 0.09 0.03 — 0.16 0.01N06603 Alloy 214 16 75 0.5 0.2 — N07214 Alloy 224 20.5 46.44 0.33 0.310.21 0.35 T_(s) sec Legierung Cu Fe P Al Zr Y B Co in ° C. Fp Alloy 6000.01 9.42 0.009 0.16 — — 0.001 — — 19.1 N06600 Alloy 601 0.04 14.4 0.0081.34 0.015 0 0.001 — 669 31.2 N06601 Alloy 690 0.01 8.45 0.005 0.31 — 00 — 720 32.7 N06690 Alloy 693 0.03 5.57 — 3.2 — — 0.002 — 939 39.9N06693 Alloy 693 0.03 4.63 — 3.08 — — 0.002 — 979 41.3 N06693 Alloy 6930.03 5.57 — 4.3 — — 0.002 — 1079 44.5 N06693 Alloy 693 0.03 5.80 — 3.27— — 0.002 — 948 40.3 N06693 Alloy 602 0.01 9.47 0.008 2.25 0.08 0.080.005 — 690 31.8 N06025 Alloy 603 0.01 9.6 0.007 2.78 0.07 0.08 0.003 —707 32.2 N06603 Alloy 214 3 — 4.5 0.1 — — 542 27.9 N07214 Alloy 22427.62 — 3.86 — — 0.38 819 38.3 All values in mass-% *) Alloy compositionfrom US Patent 4,88,125 Table 1. Legierung = Alloy; Charge = Batch

TABLE 5a Composition of the laboratory batches, Part 1. Name Chg C N CrNi Mn Si Mo Ti T G Alloy 602 CA 156817 0.171 0.036 25.2 62.1 0.06 0.070.01 0.17 T G Alloy 602 CA 160483 0.172 0.025 25.7 62.0 0.06 0.05 0.020.14 T G Alloy 601 156856 0.053 0.018 23.0 59.6 0.72 0.24 0.04 0.47 T GAlloy 690 80116 0.010 0.025 27.8 62.8 0.18 0.15 0.01 0.31 T G Alloy 690111389 0.022 0.024 28.5 62.0 0.12 0.82 <0.01 0.29 L Cr30Al1La 2297 0.0180.023 29.9 68.0 0.25 0.09 <0.01 <0.01 L Cr30Al1LaT 2300 0.019 0.021 30.267.5 0.25 0.08 <0.01 <0.01 L Cr30Al1TiLa 2298 0.018 0.022 29.9 67.5 0.250.08 <0.01 0.3 L Cr30Al1TiNbLa 2308 0.017 0.028 30.1 67.1 0.25 0.08<0.01 0.31 L Cr30Al1CLaTi 2299 0.060 0.021 30.1 67.6 0.25 0.09 <0.010.01 L Cr30Al1CLa 2302 0.049 0.02 30.1 67.1 0.28 0.09 <0.01 <0.01 E LCr30Al2La 2301 0.015 0.021 30.2 66.6 0.25 0.08 <0.01 <0.01 L Cr30Al1Ti250060 0.017 0.027 29.5 67.9 0.24 0.11 <0.01 0.31 L Cr30Al1Ti 2500630.017 0.024 29.9 67.4 0.25 0.10 <0.01 0.31 L Cr30Al1TiNb 250066 0.0160.022 29.9 67.1 0.24 0.09 <0.01 0.31 L Cr30Al1TiNb 250065 0.017 0.02530.3 67.1 0.24 0.10 0.01 0.3 L Cr30Al1TiNbZr 250067 0.019 0.020 29.767.2 0.25 0.10 0.02 0.31 L Cr30Al1TiNb 250068 0.017 0.024 29.8 66.6 0.250.09 0.01 0.31 E L Cr28Al2 250129 0.018 0.025 28.2 68.3 0.25 0.10 <0.01<0.01 E L Cr28Al2Y 250130 0.022 0.022 28.1 68.6 0.25 0.07 <0.01 <0.01 EL Cr28Al2YC1 250132 0.059 0.022 28.3 68.2 0.27 0.06 <0.01 <0.01 E LCr28Al2Nb.5C1 250133 0.047 0.022 28.3 67.7 0.25 0.06 0.01 <0.01 E LCr28Al2Nb.5C1 250148 0.049 0.019 27.9 67.9 0.25 0.07 <0.01 <0.01 E LCr28Al21C1 250134 0.048 0.026 28.2 67.1 0.25 0.09 0.02 <0.01 E LCr28Al21C1 250147 0.045 0.017 28.4 67.5 0.27 0.07 0.02 <0.01 E LCr28Al21C1Y 250149 0.054 0.020 27.9 67.2 0.27 0.06 0.01 <0.01 E LCr28Al2TiC1 250137 0.063 0.024 28.2 67.7 0.27 0.09 <0.01 0.15 E LCr28Al2TiC1 250138 0.053 0.018 28.3 68.4 0.27 0.05 <0.01 0.16 E LCr25Fe9Al3Y 250164 0.065 0.004 25.42 61.44 0.09 0.09 0.01 <0.01 E LCr25Fe9Al3C1YZrTi 250311 0.063 0.023 25.45 61.80 0.06 0.06 0.01 0.15 E LCr29Al2NbFe4 250526 0.020 0.033 29.72 63.88 0.04 0.05 0.01 0.01 T_(s)sec Name Chg Nb Cu Fe Al W in ° C. Fp T G Alloy 602 CA 156817 <0.01 0.019.6 2.36 — 683 31.9 T G Alloy 602 CA 160483 0.01 0.01 9.4 2.17 — 68331.8 T G Alloy 601 156856 0.01 0.04 14.4 1.34 0.01 669 31.2 T G Alloy690 80116 <0.01 0.01 8.5 0.14 — 683 31.4 T G Alloy 690 111389 0.01 0.018.5 0.31 — 720 32.7 L Cr30Al1La 2297 <0.01 <0.01 0.56 1.04 <0.01 73732.5 L Cr30Al1LaT 2300 <0.01 <0.01 0.54 1.3 <0.01 737 33.3 L Cr30Al1TiLa2298 <0.01 <0.01 0.55 1.28 <0.01 759 33.8 L Cr30Al1TiNbLa 2308 0.28<0.01 0.53 1.25 0.01 772 34.3 L Cr30Al1CLaTi 2299 <0.01 <0.01 0.54 1.250.01 780 32.7 L Cr30Al1CLa 2302 <0.01 <0.01 0.57 1.65 <0.01 780 33.8 E LCr30Al2La 2301 <0.01 <0.01 0.54 2.25 <0.01 809 35.6 L Cr30Al1Ti 250060<0.01 <0.01 0.54 1.15 0.01 759 33.3 L Cr30Al1Ti 250063 <0.01 <0.01 0.531.39 <0.01 759 34.2 L Cr30Al1TiNb 250066 0.31 <0.01 0.50 1.42 0.01 77234.6 L Cr30Al1TiNb 250065 0.31 <0.01 0.05 1.41 0.01 768 34.8 LCr30Al1TiNbZr 250067 0.31 <0.01 0.53 1.47 0.01 776 34.4 L Cr30Al1TiNb250068 0.88 <0.01 0.53 1.43 0.02 799 35.2 E L Cr28Al2 250129 <0.01 0.010.57 2.51 <0.01 740 34.3 E L Cr28Al2Y 250130 <0.01 <0.01 0.51 2.61 <0.01766 34.3 E L Cr28Al2YC1 250132 0.01 0.02 0.60 2.61 0.02 762 34.1 E LCr28Al2Nb.5C1 250133 0.50 0.02 0.52 2.76 0.02 800 35.2 E L Cr28Al2Nb.5C1250148 0.56 0.03 0.48 2.62 0.01 779 34.5 E L Cr28Al21C1 250134 1.06 0.030.48 2.84 0.02 850 36.1 E L Cr28Al21C1 250147 0.90 0.02 0.43 2.15 0.02774 34.3 E L Cr28Al21C1Y 250149 1.04 0.03 0.45 2.64 <0.01 800 35.1 E LCr28Al2TiC1 250137 <0.01 0.03 0.5 2.88 <0.01 788 34.9 E L Cr28Al2TiC1250138 <0.01 0.03 0.45 2.62 0.01 774 34.5 E L Cr25Fe9Al3Y 250164 <0.01<0.01 9.74 3.00 — 770 28.4 E L Cr25Fe9Al3C1YZrTi 250311 0.01 <0.01 9.462.50 — 748 28.0 E L Cr29Al2NbFe4 250526 0.15 0.01 4.00 2.04 <0.01 — 31.8All values in mass-% (T: alloy according to the prior art, E: alloyaccording to the invention, L: smelted on the laboratory scale, G:smelted on the industrial scale). Chg = Batch

TABLE 5b Composition of the laboratory batches, Part 2. Name Chg S P MgCa V Zr Co T G Alloy 602 CA 156817 0.002 0.005 0.004 0.001 0.03 0.080.05 T G Alloy 602 CA 160483 <0.002 0.007 0.010 0.002 — 0.09 0.04 T GAlloy 601 156856 0.002 0.008 0.012 <0.01 0.03 0.015 0.04 T G Alloy 69080116 0.002 0.006 0.030 0.0009 — <0.002 0.02 T G Alloy 690 111389 0.0020.005 <0.001 0.0005 — — 0.01 L Cr30Al1La 2297 0.004 0.003 0.015 <0.01<0.01 <0.002 — L Cr30Al1LaT 2300 0.003 0.002 0.014 <0.01 <0.01 <0.002<0.001 L Cr30Al1TiLa 2298 0.004 0.002 0.016 <0.01 <0.01 <0.002 <0.001 LCr30Al1TiNbLa 2308 0.002 0.002 0.014 <0.01 <0.01 <0.002 — L Cr30Al1CLaTi2299 0.003 0.002 0.015 <0.01 <0.01 <0.002 <0.001 L Cr30Al1CLa 2302 0.0030.002 0.013 <0.01 <0.01 <0.002 0.001 E L Cr30Al2La 2301 0.003 0.0020.015 <0.01 <0.01 <0.002 <0.001 L Cr30Al1Ti 250060 0.003 0.002 0.009<0.01 <0.01 <0.002 <0.001 L Cr30Al1Ti 250063 0.003 0.003 0.012 <0.01<0.01 <0.002 <0.001 L Cr30Al1TiNb 250066 0.002 0.002 0.012 <0.01 <0.01<0.002 <0.001 L Cr30Al1TiNb 250065 0.002 0.002 0.012 <0.01 <0.01 <0.002<0.001 L Cr30Al1TiNbZr 250067 0.003 0.002 0.010 <0.01 <0.01 0.069 <0.001L Cr30Al1TiNb 250068 0.002 <0.002 0.010 <0.01 <0.01 <0.002 <0.001 E LCr28Al2 250129 0.004 0.003 0.011 0.0002 <0.01 <0.002 — E L Cr28Al2Y250130 0.003 0.003 0.013 <0.0002 <0.01 <0.002 — E L Cr28Al2YC1 2501320.003 0.004 0.009 0.0012 0.01 0.003 <0.01 E L Cr28Al2Nb.5C1 250133 0.0050.003 0.009 0.0012 <0.01 0.004 0.01 E L Cr28Al2Nb.5C1 250148 0.004 0.0040.010 0.0005 0.01 — <0.01 E L Cr28Al21C1 250134 0.006 0.002 0.009 0.0009<0.01 0.006 0.01 E L Cr28Al21C1 250147 0.002 0.002 0.010 0.0005 <0.010.01 0.01 E L Cr28Al21C1Y 250149 0.004 0.005 0.013 <0.0005 <0.01 0.006<0.01 E L Cr28Al2TiC1 250137 0.005 0.004 0.008 0.0002 <0.01 0.004 <0.01E L Cr28Al2TiC1 250138 0.005 0.004 0.010 0.0002 <0.01 0.003 0.01 E LCr25Fe9Al3Y 250164 0.004 0.002 0.022 <0.001 <0.01 <0.01 0.01 E LCr25Fe9Al3C1YZrTi 250311 0.002 0.002 0.010 <0.001 <0.01 0.09 0.01 E LCr29Al2NbFe4 250526 0.003 0.002 0.012 <0.001 <0.01 <0.001 <0.01 Name ChgY La B Hf Ta Ce O T G Alloy 602 CA 156817 0.060 — 0.003 — — — 0.001 T GAlloy 602 CA 160483 0.070 — 0.003 — — — 0.001 T G Alloy 601 156856 — —0.001 — — — 0.0001 T G Alloy 690 80116 — — 0.002 — — — 0.0005 T G Alloy690 111389 — — — — — — 0.001 L Cr30Al1La 2297 <0.001 0.062 <0.001 <0.001<0.005 0.001 0.0001 L Cr30Al1LaT 2300 <0.001 0.051 <0.001 <0.001 <0.0050.001 0.001 L Cr30Al1TiLa 2298 <0.001 0.058 <0.001 <0.001 <0.005 0.0010.002 L Cr30Al1TiNbLa 2308 <0.001 0.093 <0.001 <0.001 <0.005 0.001 0.002L Cr30Al1CLaTi 2299 <0.001 0.064 <0.001 <0.001 <0.005 0.001 0.002 LCr30Al1CLa 2302 <0.001 0.057 <0.001 <0.001 <0.005 0.001 0.0001 E LCr30Al2La 2301 <0.001 0.058 <0.001 <0.001 <0.005 0.001 0.002 L Cr30Al1Ti250060 <0.001 <0.001 <0.001 <0.001 <0.005 <0.001 0.003 L Cr30Al1Ti250063 <0.001 <0.001 <0.001 <0.001 <0.005 <0.001 0.003 L Cr30Al1TiNb250066 <0.001 <0.001 <0.001 <0.001 <0.005 <0.001 0.004 L Cr30Al1TiNb250065 <0.001 <0.001 <0.001 <0.001 <0.005 <0.001 0.005 L Cr30Al1TiNbZr250067 <0.001 <0.001 <0.001 <0.001 <0.005 <0.001 0.003 L Cr30Al1TiNb250068 <0.001 <0.001 <0.001 <0.001 <0.005 <0.001 0.004 E L Cr28Al2250129 — — <0.0005 — — — 0.001 E L Cr28Al2Y 250130 0.063 — <0.0005 — — —0.001 E L Cr28Al2YC1 250132 0.07 — 0.001 — — — 0.001 E L Cr28Al2Nb.5C1250133 0.01 — — — — — 0.001 E L Cr28Al2Nb.5C1 250148 <0.01 — — — — —0.003 E L Cr28Al21C1 250134 0.01 — <0.0005 — — — 0.003 E L Cr28Al21C1250147 0.01 — 0.0012 — — — 0.001 E L Cr28Al21C1Y 250149 0.08 — 0.0012 —— — 0.002 E L Cr28Al2TiC1 250137 <0.01 — 0.0012 — — — 0.001 E LCr28Al2TiC1 250138 <0.01 — 0.0012 — — — 0.004 E L Cr25Fe9Al3Y 2501640.05 — 0.001 — — — 0.001 E L Cr25Fe9Al3C1YZrTi 250311 0.08 — 0.003 — — —0.002 E L Cr29Al2NbFe4 250526 0 — 0.003 — — — 0.003 All values in mass-%(The following values apply for all alloys: Pb: max. 0.002%, Zn: max.0.002%, Sn: max. 0.002%) (See Table 5a for the meaning of T, E, G, L).Chg = Batch

TABLE 6 Results of the tension tests at room temperature (RT), 600° C.and 800° C. The forming speed was 8.33 10⁻⁵ s⁻¹ (0.5%/min) for R_(p0.2)and 8.33 10⁻⁴ s⁻¹ (5%/min) for R_(m); KG in R_(p0.2) in R_(m) in A_(s)in R_(p0.2) in MPa R_(m) in MPa A_(s) in % R_(p0.2) in MPa R_(m) in MPaName Chg μm MPa RT MPa RT % RT 600° C. 600° C. 600° C. 800° C. 800° C.Fa Fk T Alloy 602 CA 156817 76 292 699 36 256 578 41 186 198 63.0 76.9 TAlloy 602 CA 160483 76 840 721 42 254 699 69 186 197 62.2 79.6 T Alloy601 156856 136 238 645 53 154 509 54 133 136 43.3 56.3 T Aloy 690 8011692 279 641 66 195 469 48 135 154 36.2 41.6 T Alloy 690 111389 72 285 63050 188 465 51 36.8 43.6 Cr30Al1La 2297 233 221 637 67 131 460 61 134 16733.5 43.4 Cr30Al1LaT 2300 205 229 650 71 131 469 65 132 160 33.9 46.3Cr30Al1TiLa 2298 94 351 704 69 228 490 31 149 161 39.7 51.5Cr30Al1TiNbLa 2308 90 288 683 55 200 508 39 174 181 41.6 61.0Cr30Al1CLaTi 2299 253 258 661 62 212 475 69 181 185 42.3 50.0 Cr30Al1CLa2302 212 853 673 59 233 480 59 189 194 40.0 52.9 E Cr30Al2La 2301 155375 716 66 298 504 49 275 277 33.2 55.6 Cr30Al1Ti 250060 114 252 662 67183 509 62 143 154 39.3 50.4 Cr30Al1Ti 250063 118 3252 659 70 178 510 57148 152 39.6 52.9 Cr30Al1TiNb 250066 121 240 666 67 186 498 66 245 25541.4 53.6 Cr30Al1TiNb 250065 132 285 685 61 213 521 58 264 265 41.8 64.0Cr30Al1TiNbZr 250067 112 287 692 67 227 532 65 280 280 41.6 64.2Cr30Al1TiNb 250068 174 261 666 69 205 498 65 297 336 44.9 83.2 E Cr28Al2250129 269 334 674 66 191 224 31.8 56.8 E Cr28Al2Y 250130 167 322 693 63252 522 53 220 244 32.6 57.9 E Cr28Al2YC1 250132 189 301 669 65 226 22640.2 64.0 E Cr28Al2Nb.5C1 250133 351 399 725 57 334 522 33 285 363 40.878.9 E Cr28Al2Nb.5C1 250148 365 353 704 60 284 523 58 259 344 41.2 79.5E Cr28Al21C1 250134 384 448 794 59 410 579 28 343 377 44.4 99.4 ECr28Al21C1 250147 350 372 731 57 306 547 49 309 384 43.0 89.1 ECr28Al21C1Y 250149 298 415 784 53 339 528 27 340 400 45.1 99.2 ECr28Al2TiC1 250137 142 379 745 59 327 542 29 311 314 44.0 70.4 ECr28Al2TiC1 250138 224 348 705 61 278 510 46 247 296 42.2 66.5 ECr25Fe9Al3Y 250164 117 363 731 61 310 496 28 209 210 42.2 66.7 ECr25Fe9Al3C1YZrTi 250311 505 270 678 60 207 489 56 203 211 38.1 64.6 ECr29Al2NbFe4 250526 111 313 702 64 203 521 63 147 33.7 59.9 Chg = Batch;KG = grain size

TABLE 7 Results of the oxidation tests at 1000° C. in air after 1056hours. Batch m_(gross) m_(net) Test no. m_(grutto) m_(netto) m 

Versuch in in in Name Chg Nr g/m² g/m² g/m² T Alloy 602 CA 160483 4128.66 7.83 0.82 T Alloy 602 CA 160483 425 5.48 5.65 −0.18 T Alloy 601156125 403 51.47 38.73 12.74 T Alloy 690 111389 412 23.61 7.02 18.59 TAlloy 690 111389 421 30.44 −5.70 36.14 T Alloy 690 111389 425 28.41−0.68 29.09 Cr30Al1La 2297 412 36.08 −7.25 43.33 Cr30Al1LaT 2300 41241.38 −2.48 43.86 Cr30Al1TiLa 2298 412 49.02 −30.59 79.61 Cr30Al1TiNbLa2306 412 40.43 16.23 24.20 Cr30Al1CLaTi 2308 412 42.93 −15.54 58.47Cr30Al1CLa 2299 412 30.51 0.08 30.44 Cr30Al2La 2302 412 27.25 9.57 17.68E Cr30Al1Ti 2301 412 8.43 6.74 1.69 Cr30Al1Ti 250060 421 43.30 −19.8663.17 Cr30Al1TiNb 250063 421 32.81 −22.15 54.96 Cr30Al1TiNb 250066 42126.93 −16.35 43.28 Cr30Al1TiNbZr 250065 421 25.85 −24.27 50.12Cr30Al1TiNb 250067 421 41.59 −15.56 57.16 Cr28Al2 250068 421 42.69−39.25 81.95 E Cr28Al2Y 250129 425 3.72 3.55 0.16 E Cr28Al2YC1 250130425 4.68 4.90 −0.23 E Cr28Al2Nb.5C1 250132 425 3.94 5.01 −1.07 ECr28Al2Nb.5C1 250133 425 2.56 3.98 −1.42 E Cr28Al21C1 250148 425 3.153.21 −0.07 E Cr28Al21C1 250134 425 3.34 4.23 −0.89 E Cr28Al21C1Y 250147425 2.72 2.62 0.10 E Cr28Al2TiC1 250149 425 8.44 3.84 −0.40 ECr28Al2TiC1 250137 425 3.62 4.24 −0.62 E Cr30Al1La 250138 425 3.87 4.28−0.41 E Cr25Fe9Al3Y 250164 427 5.96 4.53 1.43 E Cr25Fe9Al3C1YZrTi 250311449 4.11 4.53 −0.42 E Cr29Al2NbFe4 250526 453 5.26 4.99 0.26

indicates data missing or illegible when filed

1: A nickel-chromium-aluminum-iron alloy containing (in mass-%) >17 to33% chromium, 1.8 to <4.0% aluminum, 0.10 to 15.0% iron, 0.001 to 0.50%silicon, 0.001 to 2.0% manganese, 0.00 to 0.60% titanium, respectively0.0002 to 0.05% magnesium and/or calcium, 0.005 to 0.12% carbon, 0.001to 0.050% nitrogen, 0.0001 to 0.020% oxygen, 0.001 to 0.030% phosphorus,max. 0.010% sulfur, max. 2.0% molybdenum, max. 2.0% tungsten, the restnickel with nickel ≥50% and the common process-related impurities forthe use in solar tower power plants using nitrate salt melts as theheat-transfer medium, wherein the following relationship must besatisfied:Fp≤39.9 with  (2a)Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C   (3a)wherein Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of theelements in question in mass-%. 2: The alloy according to claim 1,especially for all components that are used are in contact with themolten salt. 3: The alloy according to claim 1, wherein the alloy isusable up to a maximum temperature of 800° C. 4: The alloy according toclaim 1, with a chromium content of >18 to 33%. 5: The alloy accordingto claim 1, with an aluminum content of 1.8 to 3.8%. 6: The alloyaccording to claim 1, with an iron content of 0.1 to 12.0%. 7: The alloyaccording to claim 1, with a silicon content of 0.001-<0.40%. 8: Thealloy according to claim 1, with a manganese content of 0.001 to 0.50%.9: The alloy according to claim 1, with a titanium content of 0.001 to0.50%. 10: The alloy according to claim 1, with a carbon content of 0.01to 0.10%. 11: The alloy according to claim 1, optionally with an yttriumcontent of 0.001 to 0.20%; a lanthanum content of 0.001 to 0.20%; acerium content of 0.001 to 0.20%; a cerium mixed metal content of 0.001to 0.20%; a zirconium content of 0.001 to 0.20%; and a hafnium contentof 0.001 to 0.20%.
 12. (canceled)
 13. (canceled)
 14. (canceled) 15: Thealloy according to claim 1, optionally with a content of niobium of 0.0to 1.1%, wherein the formula (3a) is supplemented by a term for Nb:Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+1.26*Nb+0.374*Mo+0.538*W−11.8*C  (3b)and Cr, Fe, Al, Si, Ti, Nb, Mo, W and C are the concentrations of theelements in question in mass-%.
 16. (canceled)
 17. (canceled) 18: Thealloy according to claim 1, optionally with a content of boron of 0.0001to 0.008%. 19: The alloy according to claim 1, optionally furthercontaining 0.0 to 5.0% cobalt. 20: The alloy according to claim 1,further containing at most 0.5% copper, wherein the formula (3a) issupplemented by a term for Cu:Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.477*Cu+0.374*Mo+0.538*W−11.8*C  (3c).and Cr, Fe, Al, Si, Ti Cu, Mo, W and C are the concentrations of theelements in question in mass-%. 21: The alloy according to claim 1,further containing at most 0.5% vanadium 22: The alloy according toclaim 1, wherein the impurities are adjusted in contents of max. 0.002%lead, max. 0.002% zinc, max. 0.002% tin. 23: The alloy according toclaim 1, in which the following formula is satisfied and thus aparticularly good processability is achieved: Fa□60 (4a) withFa=Cr+20.4*Ti+201*C (5a) for an alloy without Nb, wherein Cr, Ti and Care the concentrations of the elements in question in mass-%, or withFa=Cr+6.15*Nb+20.4*Ti+201*C (5b) for an alloy containing Nb, wherein Cr,Nb, Ti and C are the concentrations of the elements in question inmass-%. 24: The alloy according to claim 1, in which the followingformula is satisfied and thus a particularly hot strength/creep strengthis achieved: Fk≥47 (6a) with Fk=Cr+19*Ti+10.2*Al+12.5*Si+98*C (7a) foran alloy without B and Nb, wherein Cr, Ti, Al, Si and C are theconcentrations of the elements in question in mass-%, or withFk=Cr+19*Ti+34.3*Nb+10.2*Al+12.5*Si+98*C+2245*B (7b) for an alloycontaining B and/or Nb, wherein Cr, Ti, Nb, Al, Si, C and B are theconcentrations of the elements in question in mass-%. 25: A use of thealloy according to claim 1 as strip, sheet, wire, rod, longitudinallywelded tube and seamless tube. 26: A use of the alloy according to claim1 for the manufacture of strip, sheet, wire, rod, longitudinally weldedtube and seamless tubes.